Coming right on the heels of yesterday's post about a star so large the astrophysicists are at a loss to explain how it even exists, today we have...
... a supermassive black hole moving so fast it seems to be exceeding the escape velocity of the entire galactic cluster.
The paper about the discovery, by Yale University astronomer Pieter van Dokkum et al., appeared last week in Astrophysical Journal Letters, and its findings are hard to summarize without lapsing into superlatives. Data from the James Webb Space Telescope identified a large, rapidly-moving object from its bow shock -- the compression waves surrounding a projectile as it moves through a medium (picture the pile-up of water and resulting waves preceding a boat as it moves across the surface of a lake). But an analysis of this particular bow shock demonstrated something incredible; the object creating it was ten million times the mass of the Sun -- thus, a supermassive black hole -- and it was moving at an estimated three hundred kilometers a second.
For reference, this is over two hundred times faster than the muzzle velocity of a rifle bullet.
Amongst the many cool things about this discovery is that there is a higher-than-expected number of very young stars in the wake of this thing. Apparently, the compression caused by the black hole is triggering gas cloud collapse and star formation as it passes.
What could give something this massive that much momentum? The quick answer is "no one knows for sure," but a good candidate is a galactic merger. Two colliding galaxies represent a quantity known to astrophysicists as "a shitload of kinetic energy," and the slingshot effect -- where two moving objects pass close enough to each other that there's a transfer of momentum, causing one to slow down and the other to accelerate -- could be responsible. It might be that this was once the black hole at the center of a galaxy, but the collision caused it to swing around an even more massive black hole from the other galaxy, resulting in its being jettisoned -- not just from the combined mass of the merger, but from the entire galactic cluster.
The question that naturally comes up is "what if it was headed toward us?" Well, to start with, it's not; just a glance at the map of the bow shock should tell you that. Second, its light has a red shift of 0.96, putting it at about a billion light years away, so even if it was, it wouldn't be anything you or I would have to fret about in our lifetimes.
On the other hand, what if there was a black hole like this headed our way? Being black (as advertised), would we see it coming before the Earth was messily devoured? The answer is "almost certainly;" not only would there be the effects of the compression waves heating up the gas ahead of it, causing it to emit radiation, there'd be the fact that massive black holes cause gravitational lensing -- they bend and distort the light of objects behind them. If we were looking down the barrel of a black hole headed our way, we'd see this as an optical effect called an Einstein-Chwolson ring:
[Nota bene: black holes that are not moving toward us also cause gravitational lensing and Einstein-Chwolson rings; it'd be the combination of the lensing effect and the heating of the gas in front of the black hole that would tell us it was heading in our direction.]
Given astronomical distances, though, we still wouldn't have to worry about anything in our lifetimes. It might be bad news for our possible descendants a hundred million years from now, but there are way worse problems to concern ourselves with in the interim. And in any case, even if there was a supermassive black hole headed our way that was due to arrive either a hundred million years from now or a week from next Tuesday, there'd be absolutely nothing we could do about it. Altering the trajectory of a something with ten million times the mass of the Sun, traveling at three hundred kilometers per second, gives new meaning to the word "unfeasible." The only option, really, would be to stick your head between your legs and kiss your ass goodbye.
But like I said, the one van Dokkum et al. discovered isn't going to be a problem, even millions of years from now. It's something we can goggle at from a safe distance. A massive bullet flying through space, leaving a spangle of new stars in its wake. Yet another example of how endlessly awe-inspiring the universe is -- and the more we find out about it, the more wonderful it gets.
